You must mean favor. (Fame is something you mostly get from killing monsters, and beeing number 1 in fame is indeed the top spot of DC)

The answer to why people don't go much above 10500 favor is because you can't. Normally you lose 1% of you accumulated favor with each login, but after 10500 you start to lose 5% which effectively knocks you off the top 20. What you can do is to end at precisely 10499 on day 1 and on day 2 game like a madman to put you in top, and for a day you can claim to be number one (or at least close)

Easter egg info: If you by magical means go above 30000 favor, you start to lose 20% each login